The present invention relates to a compressed-air dryer which is used in a pneumatic pressure circuit utilizing compressed air as a source of pressure, for example, in an air brake circuit for an automotive vehicle or the like.
A compressed-air dryer of the kind referred to above normally uses regenerable desiccant material. An important enemy for the desiccant material is oil discharged from an air compressor, particularly, oil mist therein. Conventionally, as a countermeasure for the oil mist, such a technique is known that an oil-mist separator for removing the oil mist is arranged midway of a line which connects the air compressor to the compressed-air dryer, as disclosed in Japanese Utility Model Provisional Publication Nos. SHO 63-133321 and SHO 63-157234.
Further, in order to improve attachment, connection and so on of various lines, such a technique has been proposed that an oil-mist separator is arranged within a compressed-air dryer. That is, the applicant of this invention has already filed Japanese Utility Model Application No. SHO 63-166365 which discloses a compressed-air dryer. In the compressed-air dryer, a desiccant container is arranged within a housing and cooperates with the latter to define an air receiving cavity therebetween. The desiccant container has accommodated therein regenerable desiccant material. A base has one end thereof which is mounted to an open end of the housing to close the latter. The base has formed therein a recess at the other end thereof and has an inlet port which is connected to an air compressor of a pneumatic pressure circuit. The inlet port communicates with the recess. An outlet port is provided in one of the housing and the base and is connected to the air reservoir. The outlet port communicates with the air receiving cavity so that air after having passed through the desiccant container is discharged from the air receiving cavity to an air reservoir of the pneumatic pressure circuit through the outlet port. A dump valve is arranged at the other end of the base for causing the recess in the base to communicate with the ambient atmosphere in response to a command from the outside. An oil-mist separator is arranged between the desiccant container and the dump valve. The oil-mist separator has one end thereof communicating with the inlet port of the base through the recess therein. The other end of the oil-mist separator communicates with the desiccant container. The oil-mist separator removes oil in compressed air flowing from the air compressor toward the desiccant container through the inlet port and the recess.
Since, in the above compressed-air dryer, the inlet port communicates with the oil-mist separator substantially directly, the following problems arise. That is, oil droplets contained in the compressed air supplied from the air compressor enter or invade directly into the oil-mist separator so that premature deterioration occurs in the oil-mist separator. Furthermore, since the compressed air passes through the oil-mist separator under such a condition that heat generated at compression of air is not reduced sufficiently, absorption efficiency of the desiccant material, in other words, drying efficiency thereof decreases. In this respect, as disclosed in U.S. Pat. No. 4,487,617, it has been suggested that a circuitous passage is defined at the recess communicating with the inlet port to beforehand remove large oil droplets and so on, that is, before the compressed air reaches the oil-mist separator. This suggestion, however, is yet insufficient as a countermeasure for oil.
Further, as described above, the oil-mist separator is arranged between the desiccant container disposed within the housing and the dump valve disposed at the other end of the base. With the arrangement, the oil-mist separator must be mounted to and dismounted from the one end or upper end of the base.
At maintenance of the compressed-air dryer, replaced are the desiccant material within the desiccant container and a mesh element within the oil-mist separator, or the desiccant container per se containing the desiccant material and the oil-mist separator per se containing the mesh element. In this case, the desiccant container and the oil-mist separator must be mounted to and dismounted from the upper end of the base in the same direction. Accordingly, the end face of the base at the one end thereof is contaminated by the mesh element which sucks the oil. Moreover, it is not necessarily limited that the desiccant material and the mesh element are replaced simultaneously. For example, there is a case where only the mesh element is replaced. At replacement of the mesh element, in spite of the fact that only the oil-mist separator should be removed or detached, the desiccant container is also demounted. Thus, operability of the replacement is low.